This invention pertains to read-write data storage devices having parallel or concentric tracks and more particularly to a method of recovering data from a track that has been obscured or overlapped by adjoining tracks.
As bit densities and track densities are increased, the possibilities of error are also increased. Memory or data storage failure will generally shut down an entire system. The ultimate failure is a non-recoverable loss of data and to avoid this occurrence, heroic efforts are made to overcome any possibility of having a hard error from which recovery cannot be made, including rereads, head shifts and error correction codes. The final effort is to send a disk drive to the factory for special data recovery procedures.
One source of error is the overlapping or occlusion of a track by the track misregistration (TMR) of one or both adjoining tracks. The most serious condition occurs when subsequent writing of both adjoining tracks have a TMR which causes partial erasure of the intervening track. This weakens the signal from the occluded, intervening track and injects in band interference from the adjacent tracks. This condition can exceed the ability of the "built-in" recovery procedures to successfully recapture the data or even the capability of factory recovery procedures and techniques.
Another source of error is low frequency inferference caused by the lateral read back sensitivity of the recording head. Generally of low amplitude, this interference can be significant if the data on the adjacent tracks has a low frequency content and is in phase so that the interference adds up. Just one phased track on either side of the track of interest can lead to problems. The interference from phased data can cause errors even when the track registration is perfect; no occlusion of the track is necessary. Although no signal reduction occurs in the track of interest, the lateral interference can be large enough to cause read back errors.